1. Field of the Invention
The present invention relates to an imaging device and imaging method that, when carrying out shooting over a comparatively long time, generate combined image data from a plurality of image data that have been sequentially acquired during the course of shooting.
2. Description of the Related Art
It has become possible for even a novice to carry out shooting expertly and easily while confirming light trails, such as photographs of astral bodies, fireworks and light art etc. with live view, by installing image processing functions such as additive combination and comparatively bright combination in an imaging device such as a digital camera. Situations where shooting is performed to leave behind trails of light rays mainly utilize additive combination and comparatively bright combination functions.
Comparatively bright combination generates combined image data by comparing pixel values (brightness level) of pixels at the same pixel position when combining a plurality of images, and adopting bright pixels. For example, in Japanese patent laid-open No. 2013-062740 (hereafter referred to as patent publication 1) there is proposed an imaging device with which a user can take clear pictures leaving behind trails of light rays while confirming a time-lapse image at the time of shooting with live view.
Also, in Japanese patent laid-open No. 2013-172372 (hereafter referred to as patent publication 2) there is also proposed an imaging device with which image processing is changed in accordance with average brightness difference between a first image and images taken after the first image, so as to further reduce the risk of failure. Adding and averaging combination is generally known as a method that inhibits random noise. A dynamic shooting method that uses adding and averaging combination is proposed in Japanese patent application No. 5446847 (hereafter referred to as patent publication 3). An imaging device that is capable of respectively independently adjusting brightness of a background and light trails using a combination of comparatively bright combination and comparatively dark combination is disclosed in Japanese patent laid-open No. 2014-212415 (hereafter referred to as patent publication 4).
By using the imaging methods proposed in patent publications 2 and 4, it becomes easy to shoot trails of light rays. However, when shooting light trails, since processing is performed on the basis of comparatively bright combination, noise level is dominant in a first taken image. As a result, in order to obtain a combined image in which image noise has been reduced, how an initial first image is taken with low noise becomes a point at issue, and shooting with increased ISO sensitivity is difficult. Conversely, if processing is performed on the basis of adding and averaging combination to reduce noise, in places where the background is dark trails of light rays gradually become thinner every time adding and averaging processing is applied.